REU: Effects of Resource Quality and Microarthropods on Forest Floor Nitrogen Dynamics

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Resource quality is a major factor controlling rates of organic matter decomposition and nutrient release in forested ecosystems. Within the constraints of resource quality and microclimate, decomposition and nutrient dynamics are the product of faunal-microbial interactions. Activities of microarthropods generally increase decomposition rates of leaf litter and, data suggest, enhance immobilization of exogenous nitrogen. The objectives of this project are to examine the effects of resource quality on the decomposer community and on forest floor N fluxes, using 15N as a tracer, and to examine in more detail the effects of microarthropod activities on nitrogen movement. Field experiments will examine the influence of resource quality on (1) net mineralization of N from 15N-labeled litter substrates, (2) the movement of released 15N through the forest floor profile (litter N, F-layer N, soil active (microbial) N, soil slow/passive N, and soil extractable N); (3) immobilization of 15N-labeled exogenous inputs and subsequent mineralization and movement, and (4) fungal translocation of N from the soil horizon to surface litter using 15N as a tracer. In research now nearing completion, exclusion of microarthropods from decaying substrates has produced a significant effect on decomposition rates and N retention. The mechanisms for this effect will be examined in detail under more controlled conditions, by directly manipulating microarthropods in laboratory incubations, and by measuring the quantitative effects of microarthropod-microbial interactions on: (1) microbial standing stocks and total heterotrophic respiration, (2) mineralization of N from 15N-labeled litter and (3) immobilization of 15N-labeled exogenous inputs. This research group has demonstrated consistent excellence and productivity. Institutional accommodations are first-rate. Products of this research should be of importance to the better management of forest resources as well as to the fundamental understanding of forested ecosystems.